One way to kick-start the spread of green technology is for companies to make their patents available to other innovators. Toyota announced earlier this month that it was releasing 5,680 patents on its Mirai fuel cell vehicle between now and 2020, including 1,970 patents that deal with the actual fuel cell itself.

Last year, Tesla Motors CEO Elon Musk released all patents on the hot-selling Tesla electric car, stating that it was his goal to slow climate change. "It is impossible for Tesla to build electric cars fast enough to address the carbon crisis," Musk said.

But will this strategy work? Experts say that while patents can sometimes hinder the spread of green technologies by keeping innovation behind corporate doors, it's often the money and technical know-how that are the biggest obstacle to expanding the commercialization of EVs, as well as wind, solar, hydro and other renewable technologies.

"It's difficult to know why, but something good is happening here," said Estelle Derclaye, professor of intellectual property law at the University of Nottingham (UK). "This way, anybody can use (the technology). The problem is that even if the patent is out, you don't always know how to build the machine with the patent. It might not work as well."

But the real challenge is money, according to Derclaye. The dispute over green technology patents for wind turbines and solar panels has been a sticking point in recent years at the world climate negotiations.

Some developing nations say they need help if they are going to adopt carbon-free technologies that will lessen their carbon footprint, and that one way to do that is loosening intellectual property protections that keep these innovations relatively expensive.

Wealthier nations respond that they don't have the resources to build everyone a carbon-free house with solar panels, or erect wind farms in every country that wants them.

Eric Lane, a San Diego patent attorney and author of the Green Patent Blog, says that this dispute may come up again at climate talks scheduled in Paris in November 2015.

"One looming question is what, if any, intellectual property provisions will be in the next UN climate change agreement," Lane said. "In the past, there's been some dispute over whether IP should be mentioned at all. Should there be provisions for compulsory licensing or other tools to weaken IP rights driven by the perception that intellectual property is a barrier."

Lane said he doesn't believe that patents are a bottleneck to innovation or the diffusion of green technology. Unlike drug development, in which pharmaceutical companies may own a single patent that is key to manufacturing a specific medicine, there are no similar "blocking" patents in green tech.

"In the solar field, photovoltaic (panels) compete with concentrating solar," Lane said. "Silicon competes with other materials and thin film technologies." At the same time, "solar competes with wind and biofuel."

There's no one patent out there that can have the same kind of blocking effect.

Owning a patent is an important step if startup companies are to attract investors to fund their research and development.

"I suspect (the release of patents by Toyota and Tesla) will have a marginal positive benefit for research and development," Lane said. "But it's hard for me to imagine a new venture starting, growing and being successful based entirely on what is now public domain technology."